The present invention relates to an improvement in a tube for a fishing rod, having a hollow tubular member constituted of a high-strength fiber sheet such as of glass fibers, carbon fibers or amide fibers, impregnated with a synthetic resin, and a reinforcement layer of high-strength fibers wound round the hollow tubular member.
It is well known that stiffness, strength and weight, which are critical factors in fishing rods, can be controlled by using a synthetic resin reinforced with high-strength fibers such as glass fibers, carbon fibers and amide fibers as the rod material. The term "stiffness" is used here to mean characteristics such as flexural rigidity, rebounding characteristics, bending curve and so forth, while the term "strength" includes the concepts of bending strength, collapse strength and twisting strength. The weight is determined secondarily when the stiffness and the strength are satisfied by the properties of the material.
Glass fibers provide only a low resistance because such possess comparatively small strength for the weight thereof. Therefore, for obtaining high strength, the amount of material used must be increased resulting in an impractically heavy fishing rod.
For carbon fiber, the fiber bundles are arrayed in one direction to form a sheet which is lined with a thin glass woven fabric or, alternatively, woven fabric is formed by using carbon fibers as the warp and glass fibers as the weft.
When the carbon fibers are used as the warp, the rod exhibits a superior resistance to deformation along the axis because this material exhibits greater strength and resiliency than glass fibers. However, the rod has little collapse strength in the circumferential (weft) direction because the weft is constituted of glass fibers. In consequence, the rod often cracks in the longitudinal direction due to breakdown of the glass fibers constituting the weft. Similarly, the rod tends to crack by a twisting force. The cracking, needless to say, leads to breakage of the rod.
In the case of a woven fabric in which both the warp and weft are constituted of carbon fibers, the problems of longitudinal cracking and rod breakdown are avoided due to the strength against bending and circumferential compression strength. In this case, however, the carbon fibers constituting the weft exhibit excessive springing force so as to make it difficult to wind the woven fabric around a thin core metal, resulting in material which is hard to work with and a component of inferior quality.
The strength has to be selected in view of a variety of rod diameters and, hence, has to be varied according to the sections and portions of sections of the rod. To meet such a demand, the amount of the weft of specific portions of the woven fabric has to be controlled precisely during the continuous formation of the woven fabric. Such control is technically extremely difficult to effect and involves various problems in the production process.
Japanese Utility Model Publication No. 49105/1983 discloses a known fishing rod which is improved so as to obviate the above-described problems derived from the use of glass and carbon reinforcement fibers.
This known fishing rod has a core made of a preimpregnated sheet reinforced with high-strength fibers and a tape made of bundles of filaments of high-strength fibers wound around the core coarsely at a pitch which is greater than the tape width. In this fishing rod, therefore, the region around which the tape is wound and the region around which the tape is not wound exhibit completely different levels of strength against bending force. In addition, the tape wound round the core serves as a hoop so that stress is liable to be concentrated in the region on the boundary between the edges of the hoop and the portion of the core between adjacent turns of the tape, increasing the possibility of breakdown of the rod. Considering that fishing rods are usually flexed greatly in practice, this known fishing rod is not preferred because the stress is concentrated locally, particularly when the flexture is large resulting in a great possibility of breakdown of the rod, although a considerable reinforcement effect is produced when the flexture is still slight.